﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Net;
using System.Text.RegularExpressions;

namespace ProjectEulerSolutions
{
    /*
     * 
     * The nth term of the sequence of triangle numbers is given by, tn = ½n(n+1); so the first ten triangle numbers are:

1, 3, 6, 10, 15, 21, 28, 36, 45, 55, ...

By converting each letter in a word to a number corresponding to its alphabetical position and adding these values we form a word value. For example, the word value for SKY is 19 + 11 + 25 = 55 = t10. If the word value is a triangle number then we shall call the word a triangle word.

Using words.txt (right click and 'Save Link/Target As...'), a 16K text file containing nearly two-thousand common English words, how many are triangle words?

     * 
     * */
    class Problem42 : IProblem
    {
        public string Calculate()
        {
            WebClient wc = new WebClient();
            String input = wc.DownloadString("http://projecteuler.net/project/words.txt");

            var result = Regex.Matches(input, "[A-Z]+").Cast<Match>()
                .Select(x => x.Value.Sum(c => c - 'A' + 1)).Where(v => IsTriangle(v)).Count();


            return result.ToString();
        }

        bool IsTriangle(int n)
        {
            int i = 0;
            int result = 0;
            while (result < n)
            {
                i++;
                result = i * (i + 1) / 2;
                if (result == n)
                    return true;
            }

            return false;
        }
    }
}
